Hello Akshay,
Try starting both servers individually. If you can then,it may be port conflict
Below is the part of document-
Obviously, no one should be accessing the clusters during the upgrade. pg_upgrade defaults to running servers on port 50432 to avoid unintended client connections. You can use the same port number for both clusters when doing an upgrade because the old and new clusters will not be running at the same time. However, when checking an old running server, the old and new port numbers must be different.
Thanks
Rajni